Algorithm required for calculating ISIS SANS analyser efficiencies

[rbauststfc]

An algorithm is required to calculate the efficiency of the 3He analyser based on one measurement. This calculation will make use of hyperbolic functions created under issue #36137.

The algorithm will need to take a list of run numbers and also the transmission/opacity calculated from #36383. It will output the polarisation efficiency as a function of wavelength, for each run.

Under issue #36142, a step will be added later in the overall Polarised SANS workflow to take into account the time of each run to find the time-dependent polarisation efficiency.

This is required for the Polarised SANS reduction.

Calculations

• Calculate the efficiency of the cell, P, from (Tnsf-Tsf)/(Tnsf+Tsf) using data from a run, where Tnsf = T00 + T11 and Tsf = T01 + T10.
• We can then fit P = tanh(μ * pHe) to get pHe.
  • P is the measured efficiency for the given data
  • pHe is the analyser efficiency

Workflow Steps

• Inputs:
  • Run number to load
  • Period positions (++ and +- needed for this step)
  • p * d and T_E (Fit params from Transmission Calc)
• Load input run
• Calculate P using the above equation
• Fit P = tanh(μ * pHe) to get pHe
• Outputs:
  • Single spectra output for wavelength-dependent efficiency
  • Fit Params (pHe)

[dehoni]

In order to get later corrected data in absolute units, it should output the transmission of the wanted and unwanted spin state through the device as a function of wavelength, for each run. Having this the polarization efficiency is easy to calculates.